Control system for hydraulic presses



March 25,1947.

w. BECKER CONTROL SYSTEM FOR HYDRAULIQ PRES'SEZSV Filed Nov. 1S?, 1943 INVENTOR WALTER BECKER.

BYy

JW 57M.

ATTRNEYS Patented Mar. 25, 194') v UNITED ASTATES PATENTv OFFICE CONTROL SYSTEM FOR HYDRAULIC PRESSES Walter Becker, Dayton, Ohio, assignor ,to The Hydraulic Development Corporation. Inc., Wilmington, Del.,f`a tcorporation of Delaware .Application November 19, 1943, Serial No. 510,891 14 claims. (ci. lso-52) or press piston. Then, when it is desired to put the press in operation, it is necessary vfirst to re turn the ram to its full retracted or starting position.

It is customary to interconnect the press platen or ram by means of linkage with a uid flow varying device, such as the ow control member of`a variable delivery pump, whereby the ilow of fluid tothe retracting means o f the hydraulic motor is neutralized at the end of the retraction stroke of thepress. In this manner the press ram automatically comes to a halt at the end of the retraction stroke. Therefore, when the press ram settles or slides downwardly as has been previously explained, the flow controlling means operated by the linkage interconnected with the platen is shifted to direct fluid to the retraction area of the press. If the fluid is supplied by, say, a variable delivery pump, the pump will start under load due to the settling of the ram'. Irr turn, the prime mover for driving the pump will also be started under load and, in the case of an electric motor as the prime mover, expensive and complicated starting devices are required in order not to overload the power lines supplying energy tothe driving motor.

Accordingly, it is an object of this invention to provide means whereby the prime mover driving the pump may be started under no load conditions, regardless of the position occupied by the press ram.

In the operation of the press it is often .desirable suddenly to halt the press in order to pre vent possible damage to the work piece being operated, the dies or other tools mounted in the press, the press itself, or to prevent injury to an operator.

'It is, therefore, an object of this invention to provide a control system for a hydraulic circuit which is adapted suddenly to cause a cessation in the flow of pressure fluid in the system. This application is a continuation-impart of my copending application Serial No. 470,268, led December 26, 1942.

These and other objects and advantages of this invention will be more clearly apparent from the vwardly due to leakage around the driving motor 2 J following specification in connection with the drawings wherein:

Figure 1 diagrammatically illustrates one embodiment of the control system according to this invention in connection with a hydraulic press circuit, and

Figure 2 is a wiring diagram used in connection with the control system of Figure 1.

' General arrangement neutral or no delivery position, while servomoton means is connected with the pump for selectively shifting the pump into forward or retraction stroke delivery position.

The servomotor means, which may be of any standard type, preferably fluid operable, includes a valve member and a reciprocable plunger operable by pressure fluid from an auxiliary uid source, the hydraulic connection of which with said 'servomotor means is controlled by valve means or similar uid iiow controlling devices.

The pump isfconnected with a prime mover in such a manner that when the prime mover is started the pump is also started, whilethevalve means previously referred to as controlling the flow of pilot fluid to the servomotor is actuated so as to prevent the delivery of pilot fluid to the servomotor until the prime mover reaches a predetermined speed. When this speed has been reached, or after a predetermined time period has elapsed following the initiation of the starting of the prime mover, the valve means controlling the fluid connection `between the auxiliary fluid source and the servomotor is again actuated'to/ re-establish this fluid connection. The press ram, assuming that it has settled from its retracted position, is then effective, through linkage, to shift the pump on retraction stroke and thereby return the press ram to its fully retracted position. In this manner, the prime mover is permitted to come up to speed under no load, thereby protecting the prime mover, reducing the length of time required for starting and substantially reducing the power requirements for starting.

'Ihe valve means provided in the pilot fluid circuit are further 'operable by manual means whereby to prevent the delivery of fluid from the main pump at any time. In response to the actuation of said manual means, the valve means in the pilot uid circuit are actuated to exhaust the pressure fluid from the servomotor thereby per mitting the previously mentioned centering means rapidly to shift the pump to neutral or no delivery position. The pump is thus caused to cease delivering iluid suddenly and at the will of the operator and, in case a reciprocable hydraulic motor is being actuated by said nuid, the same will also suddenly stop and remain in position until the pump is again shifted on stroke. Other manual means are eiective to counteract the effeet of the rst mentioned manual means, that is, to actuate the controlv valve in the pilotdiuid circuit to again deliver pilot iluid to the/servomotor. To this end, there is provided an electric circuit, including push buttons and valve.l actuating solenoids, for controlling the actuation of the valve means in the pilot fluid circuit'.

According toanother feature of this invention, the valve means controlling the supply of iluid from the auxiliary uid source to the servomotor means is adapted, at a, predetermined point of travel of the press ram, temporarily to interrupt or by-pass the fluid flow from saidl auxiliary source to said servomotor means to bring about a temporary slow-down of the press ram. i

Structural arrangement Referring now to the drawings in detail, and in particular to Figure 1, the structure disclosed therein comprises a press kcylinderl having mounted reciprocably therein a press ram 2 which is connected to a press platen 3. The platen 3 carries an arm 4 which is adapted to engage the collar 5, adjustably mounted on a' nected to the armature I3 of a solenoid. This f solenoid I4, which is the main operating solenoid, is so arranged inl relation to the armature I3, that energization of the solenoid will cause the armature I3 to move downwardly, thereby rotating the i lever II in a clock-wise direction about the pvot I5. The .third arm of the lever I I is connected through a suitable linkage system, generally indicated at I6, with the control rod of the pump servomotor.

The pump servomotor, generally indicated at I9, comprises a double acting piston I9 within which 1s reciprocable the valve member 2B. In

turn, the valve member 20 is connected with the control rod I1, this last mentioned member being reciprocable through a bore in the end cover of the servomotor. The servomotor I8 is suitably connected to a variable delivery pump 2| in any convenient manner. The pump 2-I may be of anyv type as, for instance, a radial vpiston or a radial vane pump. the reversible type, that is, capable of delivery in both directions.

The pump is preferably of The servomotor piston I 9 has a larger diameter portion 22 reciprocable within a bore 23 off the servomotor I8'and a smaller diameter portion 24 reciprocable within the bore 25 of the servomotor I8. The smaller diameter portion 24 vis provided with a bore 26 which is in communication with the central bore 21 of the servomotor piston and the longitudinal bore 28. A second radial bore at 29 is adapted` to eiiect communication between the bore 21 and the bore 23. The valve member 20 fits within the bore l2'I and is preferably of `such a length as to exactly cover both of the radial bores 26 and 29 at one time. The valve member 20 is, therefore, adapted to uncover one of the bores 29 or 26 when it is moved from the position indicated in Figure 1.

A conduit 30 delivers pressure iiuid into the servomotor I8 at the rightihand end of the bore 23. A second conduit 3I, which includes a check valve 32, is connected from the conduit 30 into the left hand end of the bore 23 whereby uid may pass from the conduit 3| into the conduit 30 'but not vice versa. a

A conduit 33 is connected into the servomotor at the right hand end of the bore 25 and serves to conduct the exhaust fluid from the servomotor back to the reservoir or tank 34. Bores 35 are ective to establish communication between the means of a spring 3l, towards its left hand position for 'a purpose which will hereinafter become apparent.

vThe pump 2| is -further iitted with centering springs generally indicated at 38 which serve continuously to urge the pump towards no delivery position. A rod 39 is, aiiixed to the flow control member of the pump 2I and `has an enlarged diamete'r portion thereon at 40. A pair of collars 4I, slidable on rod 39, are urged by the springs 42 towards the position shown in Figure l. In this positon the collars 4I engage a fixed annular ring'43 and thereby locate the rod 39 so as to hold the flow control member of the pump in no delivery position. The servomotor piston I9 is effective to move the ow control member of the pump against the thrust of one of the springs 42 to move the pump to forward or reverse delivery.

- Pilot fluid is supplied to the pump servomotor by means of the pilot pump indicated at 44. The pump 44 draws fluid from the reservoir 34 through a conduit 45 and delivers the same at increased pressure through the conduit 46 to thefour way valve 41 from where the pilot fluid is conductedV through conduit 48 to a second four way valve 49. The valve 49 delivers th'e pilot fluid directly to the conduit 30 which is in continuous communicato the right is eiective to establish communication between conduit 48 and the exhaust conduit 52, and also to establish communication between the conduit'46 and the exhaust conduit 52, thereby by-passing the delivery of the pilot pump 44 and exhausting the servomotor I8.

The valve 49 is similarly provided with a spring 53 urging the movable valve member tothe left,

and with a solenoid 54 which is adapted, upon energization, to move said valve member to the right. Movement to the right of the valve member of .the valve- 49 is eiective to establish uid v cylinder.

l communication between the conduit 30 and the conduit 55 and between the conduits 48 and 52. The conduit 55 includes an adjustable choke valve 56 whereby therate pf exhaust from the conduit 30 to the conduit 52, when the valve member within the valve 49 is shiftedfmay be controlled.

The pilot pump 44 is further provided with the pressure reliefvalveA 51 through which the excess capacity ofthe pump 4t is discharged to exhaust when not being utilized in the operation of the servomotor orbeing by'passed through one of the valves 41, 49 to the. tank. The pilot pump 44 means of a conduit 6| with the lower portion of the press cylinder I. Connected to the conduit 60 is a conduit leading to the tonnage control valve indicated at 62, the function of which is to open the electric circuit to the mainA solenoid upon the accomplishment of a predetermined pressure within the upper portion of the press cylinder I. This valve may be of any standard design, for instance, of the type disclosed in the v United States Patent No.` 2,224,957.

Mounted in the top of the press cylinder and extending therein is a surge valve indicated by the numeral 63. This valve, likewise, may be of any standard design, for instance, of the type disclosed in the United States Patent No. 2,193,248, and is adapted, in response to the suction eiect created in the upper portion of the press cylinder I by the downward movement of the press ram 2, to open so as to admit fluid from the tank 34 to the upper portion of the cylinder I. When a predetermined pressure develops in the upper portion of the cylinder I the surge valve closes. Pilot line 64 connects from the surge valve to the conduit 6| and the surge valve is thereby adapted, in response to a predetermined pressure in the lower portion of the cylinder I to open and admit to the tank the uid from the top of the press A check valve 65 is connected to the conduit 64 and permits make-up fluid to be drawn from the tank byfthe pump during the working portionof the press stroke.

Referring now to Figure 2 wherein is illustrated the wiring diagram system of Figure 1, the electric power is supplied by two main supply lines indicated at LI and L2. The line LI has connected thereto the line 66 which is adapted to be electrically connected with the line 61 by closure of the line switch 68. The line 61 is connected through the normally closed stop switch 69 with the line 10 which in turn is connected to a line 1|. Between the lines 1| and L2 the remainder of the electrical circuit is arranged in branch lines.

blades TI and the relay coil RI with the line L2. Energization of RI causes the normally open blades RIA, RIB and RIC to close and the normally closed blades RID to open. The closure of the blades RIA provides a holding circuit for the relay coil RI which thus remains energized subsequent to the opening of the switch 12'.

with'the relay coil'R2. The energiz'ation of "the relay coil R2 is effective to close the normally open blades R2A and to thereby provide a holding Vcircuit for the relay coil R2, the motor 56 and the motor 59. This circuit will be main- `a timer indicated at T which is adapted, after the lapse of apredetermined time. to open the c blades T-| momentarily and to thereby deener- -may be driven from the shaft of the mainpump T deenergized until the switch 12 is again closed.

gize the contactor coil RI and the timer.

RIB and RIC to open while closing the blades RID. The opening of the blades RIA serves to maintain the contactor coil RI and the timer The opening of the blades-RIB has no eiect on the circuit since the relay coil R2 is maintained energized through the blades. R2A. The closing of the blades RID conditions the circuit includ'- ing the main solenoid I4 and the forward p ush button switch to be energized when said switch is closed.

The main solenoid I4 is connected between the lines L2 and 1I through the blades RID and the normally open push button 13. The push button 1.3. is by-passed by a holding circuit which includes the tonnage control switch 62A, a reversing push button 14 and a pair of normally open blades |4A. 'Ihe'blades I4A are adapted to be closed upon the energization of the main solenoid I4.

' The solenoid '5| of the valve 4,1 is connected between the lines L2 and 1| through the switch blades RIC,` the latter being by-passed by a ciry cuit including the normally openblades RSA.

The solenoid 5| is thereby adapted to be energized upon the closure of either the switch RIC or R3A.

The'relay coil R3 is connected between the blades lines L2 and'1I through the normally open emergencyv stop push button 15, which latter Aswitch is by-passed by the'normally closed push button 16 and the normally open contactor blades B3B. The last mentioned circuit provides a holding circuit whichuis eiective to maintain the coil R3 energized subsequent to the closing of the switch 15 and prior to the opening of the switch 16.

The vsolenoid 54 ofthe valve 49 is connectedv between lines L2 and 1| through the normally open limit switch 11. The switch 11 is adapted to be closed by the cam 18 carried on the platen 3 during the advancing stroke of said platen. Further advance of the platen beyond the point where the switch 11 is closed will permit the switch 11 to open, and to remain open, until the cam 13 again approaches -the switch 11 from above during the forward-travel of the press ram.

. Operation It may be assumed that all parts of the. system occupy the position shown in Figure 1, with the exception of the ram 2, which may be assumed to be settled below its fully retracted position to occupy a position intermediate its end positions so that the rod I1 and the servomotor valve 20 is movednto the left with regard to the position shown in Figure `1. It may further be assumed that the"d`riving motors 58' and 59""are at a standstill..

lf it is now desired to cause the press ram 2 toperform a working cycle, it is rst necessary The deenergization of RI permits the blades RIA, l

establishing a holding circuit for R2.

' 7 to retract the ram to its uppermost oriully retracted position, that is, to the position shown in Figure 1. To this end, the operator closes the line switch 68 and then presses starter switch 12. As a result thereof, the energizing circuit for the contator RI and the timer T is closed. Energization of the contactor coil RI closes the blades RIA and RIB thereby providing a holding circuit for RI and energizing R2. Energization of coil R2 operates to close switch RZA, thus Simultaneously, the blades RID are opened thereby insuring that the main solenoid I4 is' deenergized and will remain deenergized until the contactor coil RI is again deenergized. Also, simultaneously, the blades RIC are closed and ener-1 gize the solenoid 5I of the valve 41. The valve 41 is thereby shifted to the right by-passing the pilot iiuid from the pump 44 and exhausting the servomotor I8.

These conditions prevail until the timer T has run its predetermined period and openings the blades TI. Opening of the blades TI deenergizes the contacter coil RI and the timer T and the blades RIA. RIB and RIC are opened. The opening of the blades RIA is effective vtc maintain the coil RI in the timer T deenergized until the switch 12 is again closed to start the press in operation. The opening of the blades RIB is not effective since the coil R2 is maintained energized by its holding circuit through the blades R2A. The motors 58 and 59 continue to be energized since they are in parallel with the coil R2.

The opening of the blades RIC, simultaneously vwith the opening of RIA and RIB, is eifective to deenergize the solenoid 5I of th valve 41 thereby permitting the spring 50 to shift the valve member .leftwardly to the position shown in Figure 1. The shifting of the valve member in the valve 41 by the spring 5I) permits iuid from the pilot pump 44 to be conducted to the pump servomotor I8 where it is utilized in moving the pump to stroke against th(` thrust of the centering springs 42. Since it was assumed that the press ram 2 had settled downwardly from its tioned to shift the pump to retraction stroke and fluid would thereby be delivered through the conduit BI to the retraction area of the hydraulic motor, and the press ram would move to the position shown in Figure 1. c

The period of time during which the timer is energized, that is, subsequent to the closing of the switch 12 and prior to the opening of the blades TI, is suihcient to permit the motors 58 and 59 to come up to full speed. The driving motor or motors are, therefore, started under no load and auxiliary starting equipment is not necessary. l

If it is now desired to initiate a working cycle of the press, the, operator presses the forward push button 13 thereby energizing the main solenoid I4 and shifting the linkage I6 to put the pump on forward stroke. Energization of solepoidj|4 operates to close switch I4A and thus establish a holding circuit for solenoid I4 through tonnage switch G2 and reversing switch 14. The action of the servomotor at this time is as follows:

The valve member 20 is shifted to the right by the rod I1 against the thrust of the spring 31 and uncovers the inner .end of the radial passage 29. .Pilot fluid entering the right end of the bore 23 through the conduit 30 is thereby permitted to flow through the passage 29 and 8 the bore 21 into the left end of the bore 23. The area or the servomotor piston I9 which is exposed to the duid in the left hand side of the chamber 23 is larger than the area of the piston I9 which is exposed to the pressure fluid in the right hand end of the bore 23. The piston I5 is, therefore, urged to the right and will move rightwardly until the passage 29 is once more blocked by the valve member 20.

The pump now delivers fluid into the conduit 60 and draws duid in from the conduit tl. The iiuid drawn into the conduit 6I is removed from the retraction area of the hydraulic motor and the ram 2 moves, downwardly as rapidly as this duid is withdrawn. During this part of the forward stroke the suction created above the ram 2 is effective to open the surge valve t3 thereby permitting uid to enter the chamber above the ram 2 from the tank. After the platen has engaged the work the surge valve 63 closes and the fluid delivered by the pump into conduit 50 is effective to create pressure above the ram 2. During this part of the stroke the pump draws uid through conduit BI from the retraction area of the hydraulic motor and also through the condut 64 and the check valve 65 from the tank 3 r Upon the accomplishment of a predetermined pressure within the main cylinder I the tonnage control valve 62 is actuated to open the holding circuit of the main solenoid IB and the reversal of the press now takes place. Optionally, the holding circuit of the solenoid I4 may be operated by a limit switch (not shown) orby the reverse push button 14. In any event, deenerization of the solenoid I4 is effective to permit the spring 31 to move the valve member 20 to the left. The left end of the bore 23 is now opened to the exhaust conduit 33'through the bore 28, the bore 26, the bore 21 and the bores 35. The pressure prevailing in the right end of the bore 23 is, therefore, effective to move the servomotor piston I9 to the left to follow the movement of the valve member 20. The movement leftwardly of the piston I9 is eiective to shift the pump 2| to retraction stroke and fluid is now withdrawn from conduit 60 and driven through conduit 6l to the retraction area of the hydraulic motor. During the retraction stroke the pressure in the conduit `6I is conveyed through conduit 64 to the surge valve B3 and is effective to maintain that valve in an open position thereby permitting the fluid above the ram 2 within the cylinder I to be expelled into the tank 34. The platen moves upwardly until the control rod 6 is actuated by the f 48 and the conduit 52 thereby ley-passing the delivery of the pilot pump to exhaust, and also interconnects the conduits 30 and 55 thereby exhausting the servomotor through the choke valve 56 to conduit 52-and exhaust. The release of pilot iuid from the servomotor I8 permits the centering springs 42 to move the pump towards neutral or no delivery position. The duid expelled from the servomotor passes through the conduit to the conduit 55 and thence through the choke valve ting of the choke 56. The choke 56 isso adjusted that before the pump reaches center or no delivery position the platen has passed beyond the switch l1 and has permitted the lattervtoopen.

` The opening of the switch-11 is effective to deenergize the solenoid 54 thereby permitting the spring 53 to shift the valve member' of the'valve 49 to the left to the position shown in Figure 1 thereby re-establishing fluid connection between the pilot pump and the servomotor. Immediately upon the reestablishment of the pilot fluid circuit to the servomotor the pump is shifted on 'to stroke and the downward movement of the press ram and platen is continued. In this manner it is possible to check the rapid advance of the platen just before it engages the work whereby the shock of contact is materially reduced. The switch 17 is adapted to be effective on the downward stroke of the press ram but is ineffective on the upward stroke and thus causes no delay during the retraction stroke. v

If, at any time during the retraction or for-V wardstrokes, it is desired or necessary to bring the press ram to a suddenhaltfthe operator depresses the emergency stop switch 15. The closing of the switchl 15 energizes the contactor coil R3 which in turn closes the blades R3A and B3B. Theblades R3A are effective, when closed,

to complete a circuit between the lines 1I and L2 through the solenoidv 5| of the valve 4-1.- Energization of the solenoid 5i shifts thevalve member of the valve 41 to the right interconnecting the conduits 46 and 52 thus by-passing the delivery of the pilot pump to exhaust and also interconnects the conduits 48 and 52 thereby exhausting the servomotor i8. motor connected to exhaust the centering springs 42 are-effective rapidly to shift thepump 2i to neutral or zero delivery position. The conduit 3| and check valve 32 are effective at this time to permit rapid evacuation of the left hand end of the bore 23 should the servomotor piston be shifted from forward toward neutral.

With the pump shifted to and held in neutral by the springs 42, there is no delivery into either of the conduits 60 or 6i and,- therefore, any euuipment, such as the press ram 2, being actuated by fluid from one of the conduits will cease to operate and come to a halt. Therefore, in the device illustrated, the switch 'I5 is effective to halt the press ram 2 at any point during the forward or reverse strokes. i

The pump having been shifted to neutral by the closing of the switch 15, will remain so until the switch 16 is depressed to deenergize the coil R3. When the switch 16 is opened to deenergize the coil R3, the blades R3A and R3B will open,V

valve member 20. The switch 15 is, therefore, effective upon operation to suddenly and effectively bring the pump 2i to a neutral position and to thereby halt the flow of .uid through the associated hydraulic circuit, and the switch 'I6 effective, upon operation, to counteract the influence of the' switch 15 thus restoring' the original condition in the entire system.

It will be appreciated that the method just described for centering the pump 2i` and halting the ram 2 is more effective than would be the opening of the switches 68 or 69, inasmuch as the opening of either ofthe last mentioned switches is effective to halt the pump delivery or to stop the ram 2 only after the pumps and motors have coasted to a stop. Because of the inertia of these mem'- bers, a. vconsiderable period of time would transpire between the opening of either of the switches 88 or 69 and the. halting-of the press ram 2 or the cessation of delivery by the pump 2 I.

If desired, the pilot pump 48 may be replaced by an accumulator or other suitable source of pressure, in which case certain simplifications in the hydraulic' and electric circuit could be effected; It will be understood, however,v that the operation of this invention would not be effected by the replacement of the pilot pump 44 -by the equivalent accumulator.

It will be understood that I do not desire to be limited by the particular structure. and arrangement indicated inthe drawings but desire to comprehend such modifications as/ may come within the scope of the claims.

With the servo- Having thus fully described my invention; what I claim as. new and desire to secure by Letters Patents is: y

` 1. A hydraulic actuating system that includes avariable delivery pump, a prime mover for driving said pump, first means operable automatically 'by and upon energization oi' said prime mover to to said /control means, a prime mover'foi` actuating said source, first, means operable automatically by and upon energization of said prime mover for preventing the supply of actuating fluid to said fluid operated control means prior to said prime mover reaching a predetermined speed and means selectively operable at any time for actuating said first means to prevent the supply of actuatingfiuid to said iiuid operable iiow control means.

3. A hydraulic actuating system including a variable delivery pump,` an electric motor connected t drive said pump, pressure operable servomotor means for varying the delivery of said pump, yielding means connected to continuously urge said pump toward no-delivery position,

means automatically operable by and upon ener-y gization of said prime mover to prevent the supply ,of actuating pressure fluid to said servomotor while said electric motor is accelerating to a servomotonconnected to varyi the delivery of said' pump, centering means associated with said pump and continuously urging' said pump toward no de.. livery position, an auxiliary iiuid source for supplying actuating iluid to saidservomotor, means tor and to exhaust said servomotor, and manual means operable at will to actuate said automatically operable means and thus prevent the supply of fluid from said auxiliary source to said servomotor. y

5. In a hydraulic system, a variable delivery pump, means yieldingly urging said pump into neutral, fluid .pressure operated servomotor means connected to vary the delivery of said i' pump against the action of said yielding means,

a sourceof pressure uid for said servomotor, a prime mover connected to drive said pump, connections between said source, said servomotor, and exhaust, first valve means in said connections, operable to connect said servomotor to exhaust; means operated by and for a limited time after energization of said prime mover'to operate said first valve means, and second valve means in said connections operable at will to exhaust -said servomotor means at a predetermined desired rate.

6. A hydraulic actuating system that includes a variable delivery pump, an electric motor for driv.. ing said pump, a fluid operable servomotor for varying the delivery of said pump, centering means continuously urging said pump into and tending to hold the same in substantially neutral or no delivery position, means automatically op`- erable to prevent the supply of actuating fluid to said fluid operable servomotor prior to said electric motor attaining a predetermined speed, manual means operable selectively to prevent the supply of actuating fluid to said servomotor while simultaneously exhausting said servomotor and other means'to prevent the supply of actuating fluid to said servomotor while controllably exhausting said servomotor.

7. A hydraulic actuating system that includes a variable delivery pump, fluid operable flow control means for varying the delivery of said pump, centering means continuously urging said pump towards neutral or no delivery position, an electric motor having a driving shaft connected with the driving shaft of said pump, an auxiliary fluid source for supplying actuating fluid to said fluid operable flow control means, means automatical- 1y operable in response to the energization of said electric motor to prevent the supply of fluid from said auxiliary source to said ow control means prior to said motor attaining a predetermined minimum speed, a rst means selectively oper. able to interrupt fluid communication between said auxiliary source and said flow control meansv while freelyexhausting the latter, a second means operable to counteract said first means and thereby to restore fluid communication between said auxiliary source and s'aid flow control means, and

other means selectively operable to interrupt fluid communication between said auxiliary source and said ow control means while partially exhaustling' said servomotor whereby to permit said centering means to reduce the delivery of said pump.

8. A hydraulic actuating system that includes a variable delivery pump, a `fluid operable servomotor for varying the delivery of said pump, centering means continuously urging said pump into and ytending to' hold the same in substantially neutral or no delivery'position, an electric motor drivingly connected with said pump, a pilot pump for supplying actuating fiuid to said servomotor,

control means for. controlling. the supply of uid from said pilot pump to said servomotor, means l2 operable in response to the starting of said electric motor for actuating said control means for preventing the supply of fluid from said'pilot pump to said servomotor prior to said electric motor attaining a predetermined minimum speed, manual means selectively operable to actuate said control means to interrupt fluid communication between said pilot pump and said servomotor while freely exhausting said servomotor whereby to permit said centering means to move said pump to no delivery position, other manual means oper. able to counteract said rst mentioned manual meanswhereby to actuate said control means to restore fluid communication between said pilot pump and said servomotor whereby to move said pump into delivery position, automatic means operable to actuate said control means to interrupt fluid communication between said pilot pump and said servomotor while partially exhausting said servomotor whereby to permit said centering means to bring about a reduction in the delivery of said pump, and means for counter.. acting saidlast mentioned means whereby to restore fluid` communication between said pilot pump and said servomotor.

9. A hydraulic actuating system that includes a fluid operable reciprocating plunger. a variable delivery pump for supplying pressure fluid to said plunger for actuating the same, yielding means continuously urging said pump toward substantially neutral or no delivery position, fluid operable servomotor means for moving said pump on to stroke against'the thrust of said yielding means. a prime mover drivingly connected to said pump, an auxiliary source of pressure fluid for actuating said servomotor, valve means for controlling the supply of fluid from said auxiliary source to said servomotor, means responsive to the initiation of the starting of said prime mover for actuating said valve means to prevent the supply of iiuid from said auxiliary source to said servomotor while exhausting said J`servomotor, said means being effective over a predetermined period of time; manual means selectively operable to actuate said valve means to interrupt the supply of fluid from said auxiliary source to said servomotor while exhausting said servomotor, and means operable in response to a predetermined position of said plunger for actuating said valve means to prevent the supply of fiuid,from said auxiliary source to said servomotor while exhausting said servomotor and means associated with said last mentioned means for controlling the rate of exhaust from said servomotor.

10. In a hydraulic system, hydraulic motor means, a variable delivery pump,v yielding means urging said pump into substantially no delivery position, fluid operable servomotor means for moving said pump into delivery position against the thrust of said yielding means, pilot fluid supply means for supplying actuating iiuid to said servomotor means, an electric motor' having its driving shaft connected to the rotor of said pump. a first valve means for controlling the supplyof fluid from said pilot fluid supply means to said servomotor means and operable to prevent the supply of fluid from said pilot fluid supply means to said servomotor while permitting said 4servomotor to be freely exhausted, a second valve means for controlling the supply of fluid from said pilot fluid supply means to said servomotor means and operable to prevent the supply of uid from said pilot fluid supply means to said servomotor means while controllably exhausting said servomotor, means operable in response to the afirmarsel 11. In a hydraulic system, a uid operable re- Y ciprocable plunger, a variable delivery pump for supplying actuating uid to said plunger, yielding means continuously urging said pump into substantially no delivery position, uid operable servomotor means for selectively. moving said y 'pump into delivery position against the thrust of said yielding means, pilot uid supply means for supplying actuating uid to said servomotor means, an electric motor drivingly connected to Asaid pump, a rst means for bypassing the delivery of said pilot uid supply means while'simultaneously and freely exhausting said servomotor means, a second means for bypassing the delivery of said pilot uid supply means while simultaneously and controllably exhausting -said servomotor means, means associated with the starting circuit of said electric motor and operable in response to the energization thereof for actuating said rst means for a predetermined period of time, manual means selectively operable to actuate said rst mentioned means, other manual means operable to counteract said last mentioned manual means, means responsive to a predetermined position of forward travel of said plunger for actuating said second means. and means responsive to the continued advance of said plunger for counteracting said last mentioned means.

12. .In a hydraulic actuating system, a variable delivery pump, pressure operated means connected to vary the delivery of said pump, power means connected to drive said pump, a source of pressure, conduit meansvbetween said source and said pressure operated means and including a valve having an exhaust outlet, and means operated for a predetermined time only by and after energization of said power means, to actuate said valve, thereby to close said conduit means and s connect said pressure operated means to exhaust.

l:1'4 13. In a hydraulic system, arvariabie delivery pump, pressure-actuated control means connected to vary the delivery of said pump, power means oonnectedto drive said pump, a source of auxiliary fluid under pressure, conduit means between said source and control means and including normaily open first and second valves connected in series, said first valve being freely connected to exhaust, -means operated by and upon energization of said power means to actuate said rst valve to connect said source and said control means to exhaust, said second valve being connected to exhaust through choke means, and means operable at will to operate said second valve to exhaust said control means through said choke means.

14. In combination with a pump having pressure-operated control means for varying the delivery thereof, power means connected to drive said pump, a source of pressure iluid, a connection from said source to said control means, a valve in said connection having an exhaust connection, means operated. by and for a predetermined time after start of said power means to actuate said valveand thereby connect said control. means to exhaust, second valve means in said connection operable at will to exhaust said control means at a predetermined reduced rate, and

means yieldingly urging said pump into neutral against the operation of said controlmeans.

- WALTER BECKER.

REFERENCES CITED The following references are of record inthe ille of this patent:

UNITED STATES PATENTS 

